This invention relates to a method for generating anatomical M-Mode displays in ultrasonic investigation of living biological structures during movement, for example a heart function, employing an ultrasonic transducer.
The invention describes a technique for obtaining anatomically meaningful M-Mode displays by data extraction from 2D (two dimensional) and 3D (three dimensional) ultrasonic imaging. Conventional M-Mode is acquired along one acoustical beam of an ultrasonic transducer employed, displaying the .[.tide-variant.]. .Iadd.time-variant .Iaddend.data in a display unit with time along the x-axis and depth along the y-axis. The localization of the M-Mode line in conventional M-Mode is limited to the set of beam directions that can be generated (scanned) by the transducer.
In cardiology, the use of the M-Mode method is fairly standardized, requiring specific cuts through the heart at standard positions and angles. To be able to perform a good M-Mode measurement, important criteria are:
1. Image quality. The borders and interfaces between different structures of the heart must be clearly visible. One of the most important factors to achieve this, is to position the ultrasound transducer on the body concerned at a point where the acoustic properties are optimum. These places are often referred to as "acoustic windows". On older patients, these windows are scarce, and hard to find. PA1 2. Alignment. The standardized M-Mode measurements require that the recording is taken at specific angles, usually 90 degrees relative to the heart structure being investigated. PA1 3. Motion. As the heart moves inside the chest during contraction and relaxation, a correct M-Mode line position at one point in the heart cycle may be wrong at another point in the same heart cycle. This is very difficult to compensate for manually, since the probe must be moved synchronous to the heartbeats. Therefore, most sonographers settle for a fixed, compromise direction of the M-Mode line, i.e. transducer beam. PA1 4. Wall thickening analysis. With coronary diseases, an important parameter to observe is the thickening of the left ventricular muscle at various positions. PA1 B. Olstad, "Maximizing image variance in rendering of volumetric data sets," Journal of Electronic Imaging, 1:245-265, July 1992. PA1 E. Steen and B. Olstad, "Volume rendering in medical ultrasound imaging". Proceedings of 8th Scandinavian Conference on Image Analysis. Troms.o slashed., Norway May 1993. PA1 G. Borgefors, "Distance transformations in digital images", Computer vision, graphics and image processing 34, 1986, pp. 344-371. PA1 Peter Seitz, "Optical Superresolution Using Solid State Cameras and Digital Signal Processing", Optical Engineering 27(7) July 1988.
In many cases there can be problems getting the correct alignment at a good acoustical window. Often, the good acoustic windows give bad alignment, and vice versa. Hence, the sonographer or user spends much time and effort trying to optimize the image for the two criteria (alignment, image quality).